Co-ABPBI membranes and process for the preparation thereof

Abstract

Disclosed herein is co-ABPBI membranes comprising co-ABPBI of formula (I), Invention discloses a sol gel process for the synthesis of membranes comprising co-ABPBI of formula (I). ##STR00001##

Claims

1. A process for the preparation of a Co-ABPBI membrane comprising the steps of: a. heating polyphosphoric acid (PPA) with stirring at 100-140 C. under constant flow of nitrogen followed by addition of 50 to 99 mol. % of 3,4-diaminobenzoic acid (DABA) and 1 to 50 mol. % of dicarboxylic acid selected from formula IIIa-e to obtain a reaction mixture; wherein formula IIIa-e are shown below:
HOOC(C.sub.kH.sub.mX.sub.n)COOH Formula-IIIa where, k=1-30 containing fused aromatic ring (containing phenyl, pyridine, pyrazine, furan, quinoline, thiophene or appropriate aromatic rings containing hetero-aromatic fused ring systems) substituted with alkyl, aryl, arylene, alkylene, arylene-ether or heterocyclic groups as straight chain, branched, cyclic, aromatic or combination thereof; XO, N, S, halogen or combination thereof, n=0-10 and m=appropriate numbers of hydrogen; or ##STR00025## wherein; R.sub.1, R.sub.2H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group consisting of pyridine, pyrazine, furan, quinoline, thiopene groups; or ##STR00026## where; R.sub.1, R.sub.2, R.sub.3, R.sub.4H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group pyridine, pyrazine, furan, quinoline, thiopene groups and X is selected from the group consisting of CH.sub.2, O, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(Ph).sub.2-, CH.sub.3C(Ph)-, CH.sub.3C(isopropyl)-, CH.sub.3C(t-butyl)-, CH.sub.3C(n-propyl)-, CH.sub.3C(ethyl)- or C.sub.1-15 containing alkyl or aryl groups ##STR00027## where; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring such as pyridine, pyrazine, furan, quinoline, thiopene groups ##STR00028## where; R.sub.1, R.sub.2, R.sub.3, R.sub.4H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group consisting of pyridine, pyrazine, furan, quinoline, thiopene groups; b. increasing the temperature of the reaction mixture obtained in step (a) to 170 C. and maintaining it for 10 min to 10 hours; c. lowering the temperature of reaction mixture of step (b) to 140 C. and adding 1 to 50 mol. % tetraamine selected from formula IIa-f, while maintaining the temperature for 10 min to 5 hours; wherein formula IIa-f are shown below: ##STR00029## wherein, R.sub.1, R.sub.2 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 containing alkyl or aryl groups; or ##STR00030## wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or ##STR00031## wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or ##STR00032## wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or ##STR00033## wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups and X is selected from the group consisting of CH.sub.2, O, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(Ph).sub.2-, CH.sub.3C(Ph)-, CH.sub.3C(isopropyl)-, CH.sub.3C(t-butyl)-, CH.sub.3C(n-propyl)-, CH.sub.3C(ethyl)- or any other C.sub.1-24 containing alkyl or aryl groups; or ##STR00034## d. increasing the temperature of the reaction mixture of step (c) to 170 C., maintaining it for 10 min to 5 h, followed by raising the temperature to 190-210 C. and maintaining it for 10 min to 14 h to obtain the co-ABPBI of Formula-I, ##STR00035## wherein m and n are repeat units; R is tetraamine monomer selected from compounds of Formula IIa-f and FAR is fused aromatic ring derived from dicarboxylic acid selected from compounds of Formula IIIa-e or its positional isomers, salts or esters; e. adding water and phosphoric acid to the reaction mixture in the ratio 0:100 to 100:0 to the reaction mixture of co-ABPBI of formula-I followed by stirring for 10 min-10 h; f. degassing the solution of step (e) for 5-60 min to remove entrapped air and casting it on a support to obtain a membrane; g. keeping the membrane obtained in step (f) above in humidity chamber at 20-95% RH, 10-60 C. and 1-48 h for hydrolysis of PPA to obtain the Co-ABPBI membrane; and h. optionally vacuum drying the Co-ABPBI membrane obtained in step (g) at 40-150 C.

2. The process of claim 1, wherein in step (f) the support is selected from glass plate, glass fabric, polytetrafluoroethylene paper, and polyetheretherketone (PEEK).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: depicts sol-gel membrane of ABPBI solution in polyphosphoric acid (PPA): a. Rather than a film, crack formation occurs, which after complete sol-gel process, turns into the powdery material. b. Solution yet to undergo gelation by sol-gel process.

(2) FIG. 2: Polarization graph of MEA prepared using Co-ABPBI-2 membrane (membrane preparation given in Example 5).

(3) FIG. 3: Temperature dependent ionic conductivity of Co-ABPBI-2 membrane.

(4) FIG. 4: Stress-strain curve showing mechanical stability of Co-ABPBI-2 membrane.

SUMMARY OF THE INVENTION

(5) Accordingly, present invention provides Co-ABPBI membranes comprising co-ABPBI of formula I

(6) ##STR00003##

(7) wherein m and n are repeat units; R is tetraamine monomer having general formula II, comprising compounds of formula IIa, IIb, IIc, IId, IIe, IIf and FAR is fused aromatic ring derived from dicarboxylic acid of formula III a-e or its positional isomers, salts or esters. wherein:

(8) ##STR00004##

(9) wherein, R.sub.1, R.sub.2 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 containing alkyl or aryl groups; or

(10) ##STR00005##

(11) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or

(12) ##STR00006##

(13) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or

(14) ##STR00007##

(15) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or

(16) ##STR00008##

(17) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups and X is selected from the group consisting of CH.sub.2, O, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(Ph).sub.2-, CH.sub.3C(Ph)-, CH.sub.3C(isopropyl)-, CH.sub.3C(t-butyl)-, CH.sub.3C(n-propyl)-, CH.sub.3C(ethyl)- or any other C.sub.1-24 containing alkyl or aryl groups; or

(18) ##STR00009##

(19) and FAR (fused aromatic rings) is dicarboxylic acid having general formula III comprising compounds of formula IIIa, IIIb, IIIc, IIId and IIIe;
HOOC(C.sub.kH.sub.mX.sub.n)COOH Formula-IIIa
where, k=1-30 containing fused aromatic ring (containing phenyl, pyridine, pyrazine, furan, quinoline, thiophene or appropriate aromatic rings containing hetero-aromatic fused ring systems) substituted with alkyl, aryl, arylene, alkylene, arylene-ether or heterocyclic groups as straight chain, branched, cyclic, aromatic or combination thereof; XO, N, S, halogen or combination thereof, n=0-10 and m=appropriate numbers of hydrogen; or

(20) ##STR00010##

(21) wherein; R.sub.1, R.sub.2H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group consisting of pyridine, pyrazine, furan, quinoline, thiopene groups; or

(22) ##STR00011##

(23) where; R.sub.1, R.sub.2, R.sub.3, R.sub.4H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group pyridine, pyrazine, furan, quinoline, thiopene groups and X is selected from the group consisting of CH.sub.2, O, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(Ph).sub.2-, CH.sub.3C(Ph)-, CH.sub.3C(isopropyl)-, CH.sub.3C(t-butyl)-, CH.sub.3C(n-propyl)-, CH.sub.3C(ethyl)- or C.sub.1-15 containing alkyl or aryl groups.

(24) ##STR00012##

(25) where; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring such as pyridine, pyrazine, furan, quinoline, thiopene groups.

(26) ##STR00013##

(27) where; R.sub.1, R.sub.2, R.sub.3, R.sub.4H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group consisting of pyridine, pyrazine, furan, quinoline, thiopene groups

(28) In an embodiment, present invention provides a process for the preparation of Co-ABPBI membranes comprising the steps of a. heating PPA with stirring at 100-140 C. under constant flow of nitrogen followed by addition of 50 to 99 mol. % of 3,4-diaminobenzoic acid (DABA) and 1 to 50 mol. % of dicarboxylic acid of formula III(a-e) to obtain the reaction mixture; b. increasing the temperature of the reaction mixture obtained in step (a) slowly to 170 C. and maintaining it for 10 min to 10 hours; c. lowering the temperature of reaction mixture of step (b) to 140 C. and adding 1 to 50 mol. % tetramine of formula II(a-f), while maintaining the temperature for 10 min to 5 hours and; d. increasing the temperature of the reaction mixture of step (c) to 170 C., maintaining it for 10 min to 5 h, followed by raising the temperature to 190-210 C. and maintaining it for 10 min to 14 h to obtain the co-ABPBI of Formula-I. e. adding water and phosphoric acid to the reaction mixture in the ratio 0:100 to 100:0 to the reaction mixture of co-ABPBI of formula-I followed by stirring for 10 min-10 h; f. degassing the solution of step (e) for 5-60 min to remove entrapped air and casting it on an appropriate support such as glass plate, or glass fabric, or Teflon paper, or Polyetheretherketone (PEEK) g. keeping the membranes obtained in step (f) above in humidity chamber at 20-95% RH, 10-60 C. and 1-48 h for hydrolysis of PAA to obtain the membranes; and h. optionally vacuum drying the hydrolyzed membranes obtained in step (d) at 40-150 C. to obtain the desired product.

(29) In yet another embodiment of the present invention, said membrane is useful for electrochemical devices including fuel cell, supercapacitor, etc. and for liquid and gas separations.

DETAILED DESCRIPTION OF THE INVENTION

(30) The present invention provides co-ABPBI membranes comprising co-ABPBI of formula I

(31) ##STR00014##

(32) Wherein m and n are repeat units;

(33) The co-ABPBI is a copolymer of formula I, derived from 3,4-diaminobenzoic acid, R is tetraamine monomer having general formula II, comprising compounds of formula IIc, IId, IIe, IIf and FAR is fused aromatic ring derived from dicarboxylic acid of formula III (a)-III(e) or its positional isomers, salts or esters.

(34) wherein:

(35) ##STR00015##

(36) wherein, R.sub.1, R.sub.2 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 containing alkyl or aryl groups; or

(37) ##STR00016##

(38) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or

(39) ##STR00017##

(40) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or

(41) ##STR00018##

(42) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups; or

(43) ##STR00019##

(44) wherein, R.sub.1, R.sub.2, R.sub.3, R.sub.4 is selected form a group consisting of H, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-24 alkyl or aryl groups and X is selected from the group consisting of CH.sub.2, O, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(Ph).sub.2-, CH.sub.3C(Ph)-, CH.sub.3C(isopropyl)-, CH.sub.3C(t-butyl)-, CH.sub.3C(n-propyl)-, CH.sub.3C(ethyl)- or any other C.sub.1-24 containing alkyl or aryl groups; or

(45) ##STR00020##

(46) and FAR (fused aromatic rings) is dicarboxylic acid having general formula III comprising compounds of formula IIIc, IIIb, IIIc, IIId and IIIe;
HOOC(C.sub.kH.sub.mX.sub.n)COOH Formula-IIIa

(47) where, k=1-30 containing fused aromatic ring (containing phenyl, pyridine, pyrazine, furan, quinoline, thiophene or appropriate aromatic rings containing hetero-aromatic fused ring systems) substituted with alkyl, aryl, arylene, alkylene, arylene-ether or heterocyclic groups as straight chain, branched, cyclic, aromatic or combination thereof; XO, N, S, halogen or combination thereof, n=0-10 and m=appropriate numbers of hydrogen; or

(48) ##STR00021##

(49) wherein; R.sub.1, R.sub.2H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group consisting of pyridine, pyrazine, furan, quinoline, thiopene groups; or

(50) ##STR00022##

(51) where; R.sub.1, R.sub.2, R.sub.3, R.sub.4H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group pyridine, pyrazine, furan, quinoline, thiopene groups and X is selected from the group consisting of CH.sub.2, O, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(Ph).sub.2-, CH.sub.3C(Ph)-, CH.sub.3C(isopropyl)-, CH.sub.3C(t-butyl)-, CH.sub.3C(n-propyl)-, CH.sub.3C(ethyl)- or C.sub.1-15 containing alkyl or aryl groups.

(52) ##STR00023##

(53) where; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring such as pyridine, pyrazine, furan, quinoline, thiopene groups.

(54) ##STR00024##

(55) where; R.sub.1, R.sub.2, R.sub.3, R.sub.4H, OH, O-alkyl, CH.sub.3, CF.sub.3, F, Cl, Br, I, NO.sub.2 or C.sub.1-15 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring selected from group consisting of pyridine, pyrazine, furan, quinoline, thiopene groups.

(56) The process for the synthesis of Co-ABPBI compound of Formula I and membranes thereof comprises following steps: a. heating PPA with stirring at 100-140 C. under constant flow of nitrogen followed by addition of 3,4-diaminobenzoic acid (DABA) and dicarboxylic acid of formula III(a-e) to obtain the reaction mixture; b. increasing the temperature of the reaction mixture obtained in step (a) slowly to 170 C. and maintaining it for 10 min to 10 hours; c. lowering the temperature of reaction mixture of step (b) to 140 C. and adding tetramine of formula II(a-f), while maintaining the temperature for 10 min to 5 hours and; d. increasing the temperature of the reaction mixture of step (c) to 170 C., maintaining it for 10 min to 5 h, followed by raising the temperature to 190-210 C. and maintaining it for 10 min to 14 h to obtain the co-ABPBI of Formula-I. e. adding water and phosphoric acid to the reaction mixture in the ratio 0:100 to 100:0 to the reaction mixture of co-ABPBI of formula-I followed by stirring for 10 min-10 h; f. degassing the solution of step (e) for 5-60 min to remove entrapped air and casting it on an appropriate support such as glass plate, or glass fabric, or Teflon paper, or Polyetheretherketone (PEEK) g. keeping the membranes obtained in step (f) above in humidity chamber at 20-95% RH, 10-60 C. and 1-48 h for hydrolysis of PAA to obtain the membranes; and h. optionally vacuum drying the hydrolyzed membranes obtained in step (d) at 40-150 C. to obtain the desired product.

(57) In the instant invention, co-ABPBI is synthesized using 3,4-diaminobenzoic acid, 3,3-diaminobenzidine and naphthalene dicarboxylic acid (in varying proportions) in PPA as the solvent. Membranes were casted from this copolymer solution on suitable substrate such gas glass plate, or glass fabric, or Teflon paper, etc. and phased out in controlled humidity and temperature conditions. The hydrolyzed membranes were then optionally vacuum dried. Due to the incorporation of rigid naphthalene following benefits/advantages were achieved: a. Co-ABPBI solution in PPA could be used immediately after its synthesis for membrane preparation by sol-gel process. Thus the following are avoided: polymer isolation, its purification, re-dissolution, membrane casting involving solvent evaporation or immersing in nonsolvent such as water solution and then doping with phosphoric acid; reducing number of steps as known in the literature. b. The membrane could be prepared by sol-gel method in the film form, without powder formation; as usually found without use of naphthalene dicarboxylic acid. Thus formed sol-gel membranes showed membrane forming ability possessing excellent mechanical strength of the membrane with do not tear easily. c. The acid content may be tuned by varying sol-gel conditions.

(58) The synthesized Co-ABPBI membrane is characterized by the inherent viscosity, doping level analysis, ionic conductivity, mechanical property and fuel cell performance.

(59) In another embodiment, the membrane disclosed herein finds application in various areas of filtration, fuel cells, super capacitors, Li-ion batteries and others. With reference to example 6 and FIG. 2, it may be apparent to one skilled in the art that the membrane of the invention provides enhanced fuel cell performance.

EXAMPLES

(60) Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1

Synthesis of Co-ABPBI-1

(61) A three-neck round flask equipped with a mechanical stirrer, N.sub.2 inlet and outlet was charged with 230 g of PPA and heated with stirring above 140 C. under constant flow of nitrogen. A 10 g (66 mmol) of 3,4-diaminobenzoic acid and 0.71 g (3.28 mmol) of 2,6-naphthalene dicarboxylic acid was added to the reaction mixture. The temperature was slowly raised to 170 C. and maintained for 3 h and 30 min. The temperature was lowered down to 140 C. and 0.70 g (3.28 mmol) of 3,3-diaminobenzidine (DAB) was added while maintaining the temperature for 30 min. The temperature was then raised to 170 C. for 1 h. Further, the temperature was increased to 200 C. and maintained for 2 h 55 min. After polymerization, 52.5 g of phosphoric acid was added and stirred for 2 h 25 min. The solution was then degassed for 30 min to remove entrapped air.

Example 2

Preparation of Membrane Using Reaction Mixture of Co-ABPBI-1

(62) The reaction mixture as prepared in Example 1 was poured on a clean surface and casted using a doctor's knife. The membranes were kept in humidity chamber at 60% RH and 35 C. for 15 h for hydrolysis of PAA. Some of the hydrolyzed membranes were vacuum dried at 100 C. For viscosity measurement, small amount of polymer was precipitated in stirred water. The precipitated polymer was then crushed, water washed, treated with aqueous sodium hydroxide and again washed with water. It was further dried at 100 C. under vacuum for 7 days. Inherent viscosity of Co-ABPBI-1 was measured using 0.2 g/dL solution in conc. H.sub.2SO.sub.4 at 35 C. The viscosity of obtained polymer was 3.6 dL/g. For doping level analysis, three small samples of the dried membrane were kept in 0.3 M NaOH solution for a 24 hrs. The change in the concentration of NaOH was determined by 0.2N oxalic acid. These samples were vacuum dried at 100 C. for 5 days. The doping level of the membrane was 8.1 mol/RU.

Example 3

Preparation of Membrane Using Reaction Mixture of Co-ABPBI-1

(63) The reaction mixture as prepared in Example 1 was poured on a clean surface and casted using a doctor's knife. The membranes were kept in humidity chamber at 40% RH and 27 C. for 15 h for hydrolysis of PAA. Some of the hydrolyzed membranes were vacuum dried at 100 C. For viscosity measurement, small amount of polymer was precipitated in stirred, water. The precipitated polymer was then crushed, water washed, treated with aqueous sodium hydroxide and again washed with water. It was further dried at 100 C. under vacuum for 7 days. Inherent viscosity of Co-ABPBI-1 was measured using 0.2 g/dL solution in conc. H.sub.2SO.sub.4 at 35 C. The viscosity of obtained polymer was 3.0 dL/g. For doping level analysis, three small samples of the dried membrane were kept in 0.3 M NaOH solution for a 24 hrs. The change, in the concentration of NaOH was determined by 0.2 N oxalic acid. These samples were vacuum dried at 100 C. for 5 days. The doping level of the membrane was 25.1 mol/RU.

Example 4

Synthesis of Co-ABPBI-2

(64) A three-neck round flask equipped with a mechanical stirrer, N.sub.2 inlet and outlet was charged with 230 g of PPA and heated with stirring above 140 C. under constant flow of nitrogen. 10 g (66 mmol) of 3,4-diaminobenzoic acid (DABA) and 1.42 g (6.56 mmol) of 2,6-naphthalene dicarboxylic acid was added to the reaction mixture. The temperature was slowly raised to 170 C. and maintained for 3 h 30 min. The temperature was lowered down to 140 C. and 1.4 g (6.56 mmol) of 3,3-diaminobenzidine (DAB) was added while maintaining the temperature for 30 min. The temperature was then raised to 170 C. for 1 h. Further, the temperature was increased to 200 C. and maintained for 5 h 15 min. After polymerization 82.4 g of phosphoric acid was added and stirred for 3 h 30 min. The solution was then degassed for 60 min to remove entrapped air.

Example 5

Preparation of Membrane Using Reaction Mixture of Co-ABPBI-2

(65) The reaction mixture was poured on a clean surface and casted using a doctor's knife. The membranes were kept in humidity chamber at 80% RH, 35 C. and 24 h for hydrolysis of PAA. The hydrolyzed membranes were vacuum dried at 100 C. For viscosity measurement, small amount of polymer was precipitated in stirred water. The precipitated polymer was then crushed, water washed, treated with aqueous sodium hydroxide and, again washed with water. It was further dried at 100 C. under vacuum for 7 days. Inherent viscosity of Co-ABPBI-2 was measured using 0.2 g/dL solution in conc. H.sub.2SO.sub.4 at 35 C. The viscosity of obtained polymer was 2.94 dL/g. For doping level analysis, three small samples of the dried membrane were kept in 0.3 M NaOH solution for a 24 hrs. The change in the concentration of NaOH was determined by 0.2N oxalic acid. These samples were vacuum dried at 100 C. for 5 days. The doping level was estimated by both methods, titrimetry as well as gravimetry analysis. The doping level of the membrane was 6 mol/RU.

Example 6: Electrochemical Performance of Co-ABPBI-2 Membrane Based MEA (Membrane Electrode Assembly)

(66) Membrane electrode assembly (MEA) was made by sandwiching the membrane prepared as given in Example 5 in between two electrodes prepared with the known prior art. The active area for MEA was 9 cm.sup.2. The polarization graph is shown in FIG. 2, which shows that the current density at 0.6 volt is 2000 mA/cm.sup.2 and peak power density is 1512 mW/cm.sup.2.

Example 7: Ionic Conductivity of Co-ABPBI-2 Membrane

(67) Ionic conductivity measurements were performed by AC impedance technique, in which membrane is sandwiched between platinum electrodes. Impedance spectra were recorded over the frequency range of 1 MHz to 0.1 Hz with potential amplitude of 10 mV at different temperatures in the range of 30-150 C. The measurements were all performed in a thermo-controlled cell under anhydrous conditions. The conductivity () was calculated as follows:

(68) $=\frac{L}{RA}$

(69) Where R, L, and A are the measured resistance, thickness, and cross-sectional area of the membrane, respectively. The proton conductivity results are shown in Table 1 and FIG. 3.

(70) TABLE-US-00001 TABLE 1 Ionic conductivity of Co-ABPBI-2 membrane Temperature Ionic conductivity ( C.) (S/cm) 30 0.0150 50 0.0174 70 0.0216 90 0.0248 110 0.0275 130 0.0293 150 0.0352

Example 8: Mechanical Properties of Co-ABPBI-2 Membrane

(71) Mechanical property analyses were performed using a micro-tensile tester at room temperature and the measurements were repeated for seven samples for reproducibility. The samples were kept between the holders, tightened up to 40 Ncm and were subsequently pulled at a speed of 100 m s.sup.1. Obtained stress-strain curve is shown in FIG. 4.

Advantages of the Invention

(72) 1. Process for sol-gel membranes skips several steps involved in conventional solution casting of ABPBI that involves evaporation of corrosive acidic solvents. 2. Membrane preparation by sol-gel has higher mechanical strength for the acid doped membranes and is due to incorporation of rigid aromatic structure. 3. Invention provides ease of casting. 4. The instant process allows to vary acid content in the formed membrane by merely varying sol-gel parameters.